Heat shield for an oven control



Jan. 30, 1968 M. A. RONK 3,366,330

HEAT SHiELD FOR AN OVEN CONTROL Filed March 50, 1966 WITNESSES v INVENTOR ZZMM Murmy RQnk United States Patent 3,366,330 HEAT SHIELD FOR AN OVEN (ZONTROL Murray A. Bonk, Fredericktown, Ghio, assignor to Westinghmuse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Mar. 30, 1966, Ser. No. 538,754 6 Claims. (Cl. 236-15) This invention relates generally to temperature control of cooking ovens.

The ordinary hydraulic sensing element normally used in cooking ovens is adversely affected by oven temperatures substantially higher than the usual temperatures to which the member is subjected in normal cooking operations. Thus, the cooking ovens which are of the type adapted for a heat-cleaning operation, in which food soil is burned off the interior of the oven with temperatures well above the usual 550 to 600 F. maximum, require either another type of sensing element (usually of a more costly type), or the sensing element must be protected during the heat cleaning operation.

This invention is concerned both with protection of an ordinary hydraulic sensing element, and with temperature control of the oven exercised in accordance with the quality of protection afforded the element.

It is contemplated in accordance with the invention, that the sensing element be protected from the high oven temperatures by shielding means substantially covering the hydraulic sensing element. The shielding means is adapted to contain a porous material saturated with a liquid. The temperature controls for the oven are set at a temperature above the boiling point of the liquid in the shielding means so that until the liquid is substantially evaporated out of the shielding means the sensing member continues to sense a temperature approximating the boiling point of the liquid. For example, if the currently preferred liquid, ordinary tap water, is used to saturate the porous material within the shielding means, the sensing element will sense a temperature of about 212 F. until at least a substantial part of the water is evaporated from the interior of the shielding means. During this period the oven thermostatic control may be set at, say, 250' F., which is not sensed by the element until a large part of the water has been evaporated. During the period of evaporation the oven temperature rises well above values that the sensing element would normally withstand, and heat cleaning of the oven interior is effected during this period.

After the water has evaporated, the sensing element temperature rises to 250 and, being satisfied, deenergizes the heating means in the oven. While the sensing element temperature continues to rise because of the residual heat in the oven, the oven temperature drops to a level approaching normal cooking temperatures so there is no danger of the sensing element being damaged by overheat.

It will be appreciated from the foregoing that this arrangement not only provides protection for the ordinary hydraulic sensing element, but also provides a simple method of control of oven temperatures for a heat cleaning operation.

The invention will be explained in more detail in connection with the accompanying drawing illustrating a preferred embodiment of the invention by way of example and wherein:

FIGURE 1 is an isometric view of a part of an oven interior;

FIG. 2 is a face view of one form of shielding means;

FIG. 3 is a sectional view corresponding to one taken along the line IIIIII of FIG. 2;

FIG. 4 is a view of the interior of the oven with the "ice shielding means placed in protecting relation about the sensing member or thermostat in the oven; and

FIG. 5 is a simplified circuit diagram of the temperature control and heating means for the oven cavity.

The oven liner parts of the oven cavity shown in the drawing include a side wall 12, top wall 14, bottom wall 15, rear wall 16, and a peripheral front border 18 framing the open front of the cavity and against which the oven door 20 closes. The top heating element 22 is shown in part adjacent the top wall 14. A conventional hydraulic-type, thermostatic element including a hollow, elongated bulb 24 connected to a capillary tube 26 at its rear end, may be disposed in a typical location to extend in a front-to-rear direction in the upper right-hand corner of the oven cavity. The bulb can be conventionally supported from the side wall 12 by a pair of readilydetachable spring clips 28. The capillary tube 26 extends through a grommet 30 in the rear wall of the oven for connection to a controller which is part of the temperature control system for the oven. While the shielding means 32 for the bulb may take various forms in accordance with the invention, its presently preferred form is illustrated in FIGS. 2 and 3. As such, it generally comprises a series of concentrically arranged tubes having porous material in separate layers in the annular spaces between adjacent tubes. The porous material is adapted to be saturated with a liquid such as water. In the embodiment shown as an example, three tubular members 34, 36 and 38 of about the same length but of different diameters are used. The outer tube 34 has one closed end 40 and a generally open end 42. The annular layers of porous material 44 extend from endto-end of the tube with the center layer having a central longitudinal hollow core 46 to receive the bulb 24 when the shielding means is slipped into its operating position over the bulb. The shielding means can be made of relatively inexpensive material such as aluminum tubes 3448 packed with ordinary glass fiber material of the same type used to insulate the oven. Other materials having similar characteristics of course may be used to make a satisfactory protective shield.

The shielding means performs a dual role during the operation of the oven according to the invention. First, it protects the bulb from overheating during periods when the temperature in the oven is above that normally acceptable to the bulb. Second, it serves a control function with the sensing bul-b by delaying the deenergization of the heating means for the oven during a heat cleaning operation until substantially all of the liquid in the shielding means has boiled oif.

Water is the preferred liquid used to saturate the porous mass in the shielding means. The shielding means is filled with an amount of water which substantially saturates the packing and is then installed by first removing the supporting clips 28 for the bulb, and then slipping the shielding tube over the bulb with the bulb being received in the core 46 of the tubes. The shield is supported by suitable means such as a pair of auxiliary clips 43 (FIG. 4) which project inwardly from the side wall 12 of the oven and which may be removable if desired. The shield in its installed position is best shown in FIG. 4.

The energization and temperature control means and circuit for an oven with which the invention may be used is substantially conventional and is generally illustrated in FIG. 5. The sensing bulb 24 is connected through the capillary tube 26 to actuate a controller 50 which includes switch means for controlling energization of the top heater 22 and the bottom heater 52 in accordance with the desired cooking operation. Specific oven temperatures are set, as is conventional, by adjusting knob 54. The oven circuit is connected to a power source such as 236 volts through a box 56 representing typical power switch means connected to lines L1 and L2 and the neutral line. No further description of the energization and temperature control arrangement is deemed necessary for an understanding of the inventive concept to be had since the invention is operable in an environment afforded by the typical conventional oven However, certain supplemental means such as door interlocks, signal lights are preferably provided in connection with the control circuit for safety. Also, of course, the oven structure itself may have additional insulation and ventilating means to insure that exterior surfaces do not reach temperatures exceeding those established by Underwriters Lab. for safe operation. However, the workings of the invention will be appreciated and easily understood from the environmental information so far disclosed.

To perform a heat cleaning operation of the oven, the shielding means is first saturated with water and placed over the bulb as previously noted. The temperature setting for the oven is established by adjusting the temperature control means to a temperature in excess of the boiling point of the liquid. In the preferred example wherein the liquid in water, the liquid is water, the temperature setting may be adjusted to, say, 250 F. assuming a boiling point of the water of 212 F. The 250 F. setting is in the bake range, and accordingly the bottom element 52 will be fully energized and the top element 22 energized at half voltage under typical conditions. The oven temperature rises in an attempt to satisfy the 250 F. setting of the control. As the oven temperature reaches and exceeds the boiling point of the water in the shielding means, the water boils and escapes into the oven. While the water boils the bulb 24 senses that boiling point temperature and assumes that the oven temperature is unsatisfied. Thus, the temperature of the oven continues to rise into the heat cleaning range which is well above the normally acceptable temperatures for the bulb. After substantially all of the water has evaporated,-the bulb temperature begins to rise as the heat penetrates and raises the temperature of the interior of the shielding means. When the bulb senses a temperature corresponding to the temperature setting of the controller, say the 250 F., the controller deenergizes the oven heating means. The oven temperature at this time is in the heat cleaning range which is substantially above the temperature which the bulb can withstand. Accordingly, the bulb temperature continues to rise, but the oven temperature falls at the same time, Thus, by the time the bulb reaches the oven temperature, the oven temperature will be at a level which the bulb can withstand.

It will be appreciated that the shielding provided by the shielding means does not stop immediately when the Water is evaporated. The use of an insulating material such as the ordinary glass fiber insulation for ovens provides additional shielding for the bulb after the water has evaporated and delays the rate at which the temperature of the bulb increases.

The compartmented construction of the shielding means is believed to provide a reduced rate of evaporation of the water by interfering with the free movement of the water vapor. It is also to be appreciated that the construction of the shielding means for purposes of example is that which is now deemed most practical from a cost and usage standpoint. However, the construction can vary considerably such as providing interior compartments of a different configuration, providing perforations between compartments and like departures in design.

The shielding characteristics of the shielding means are determined in accordance with such factors as the heat loss rate of the oven and wattage of the heaters. The quantity of liquid which the shielding means holds is determined in accordance with the length of time the particular oven should be in a heat cleaning temperature range so that by the time the liquid is substantially all evaporated and the heating means deenergized, the larger part of the heat cleaning job has been completed.

It is preferred that the oven beset to a temperature for this type of heat cleaning operation which is only slightly above the boiling point of the water. This provides a substantial safety margin for the bulb by terminating the heating of the oven when the bulb is at a temperature well below the maximum temperature it can withstand.

The advantages of the invention can be readily appreciated in light of the foregoing description. First, protection during the heat cleaning operation is provided for the relatively inexpensive, conventional, hydraulic sensing bulb. Heat cleaning can be accomplished while using the conventional temperature control and energization arrangements of conventional ovens. Since the shielding means is detachable, its use is not restricted to a single oven. With the oven temperature set at a relatively low level, failure to remove the shielding means after the heat cleaning cycle has terminated results in the oven temperature being controlled at the relatively low set temperature.

What is claimed is:

1. In an oven:

thermostatic means;

shield means for substantially covering said thermostatic means when a heat cleaning operation is to be carried out;

said shield means including means adapted to be satuated with a liquid for delaying the response of said thermostatic means to an actual oven temperature in excess of the boiling temperature of said liquid until at least a substantial portion of said liquid has boiled OH.

2. A system according to claim 1 including:

means partitioning the interior of said shield means into at least two separated spaces containing said saturable means.

3. A system according to claim 2 wherein:

said partition means separates said interior into concentrically-arranged spaces about a central hollow core receiving said thermostatic means.

4. A system according to claim ll wherein:

said thermostatic means is in the form of a long bulb of the hydraulic type; and

said shield means is in the form of a long tubular member having concentrically arranged and separated masses of fibrous insulating material therein.

5. The method of protecting the thermostat of oven temperature control means while heating said oven interior to temperatures above a normally acceptable temperature for said thermostat, comprising the steps:

placing a shielding member including a liquid saturated porous mass about said thermostat;

adjusting said oven temperature control means to an oven temperature setting in excess of the boiling temperature of said liquid; and

applying heat to said oven to produce temperatures in said oven well above said temperature setting until suflicient liquid is evaporated to permit said thermostat to rise to said temperature setting and thereby terminate said application of heat.

6. The method of claim 5 wherein:

adjusting said oven temperature control means to a temperature setting which is only slightly in excess of the boiling temperature of said liquid to permit a substantial rise in temperature of said thermostat after said liquid is evaporated.

References Cited UNITED STATES PATENTS ROBERT A. OLEARY, Primary Examiner.

W. E. WAYNER, Assistant Examiner. 

5. THE METHOD OF PROTECTING THE THERMOSTAT OF OVEN TEMPERATURE CONTROL MEANS WHILE HEATING SAID OVEN INTERIOR TO TEMPERATURES ABOVE A NORMALLY ACCEPTABLE TEMPERATURE FOR SAID THERMOSTAT, COMPRISING THE STEPS: PLACING A SHIELDING MEMBER INCLUDING A LIQUID SATURATED POROUS MASS ABOUT SAID THERMOSTAT; ADJUSTING SAID OVER TEMPERATURE CONTROL MEANS TO AN OVEN TEMPERATURE SETTING IN EXCESS OF THE BOILING TEMPERATURE OF SAID LIQUID; AND APPLYING HEAT TO SAID OVEN TO PRODUCE TEMPERATURES IN SAID OVEN WELL ABOVE SAID TEMPERATURE SETTING UNTIL SUFFICIENT LIQUID IS EVAPORATED TO PERMIT SAID THERMOSTAT TO RISE TO SAID TEMPERATURE SETTING AND THEREBY TERMINATE SAID APPLICATION OF HEAT. 